1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a protective circuit module for a secondary battery having improved mountability and configuration.
2. Discussion of Related Art
In general, a secondary battery is a rechargeable battery. High performance secondary batteries are divided into Ni-MH secondary batteries and lithium secondary batteries. Lithium secondary batteries include lithium metal secondary batteries, lithium ion secondary batteries (polygon type, cylinder type, and pouch type), lithium ion polymer secondary batteries, and lithium polymer secondary batteries.
Power demands of small secondary batteries are greater due to such batteries being used to power mobile telephones, laptop computers, and personal digital assistants. Lithium ion secondary batteries and lithium ion polymer batteries are the most commonly used lithium secondary batteries.
Lithium ion secondary batteries generally have a greater stability than lithium metal secondary batteries. However, since the main components of such batteries (such as a positive electrode, a negative electrode, and an electrolyte) are combustible, various safety apparatus are mounted in the battery to improve stability.
For example, a positive temperature coefficient (PTC) material may be used as a safety device. When a temperature rises above a certain threshold in the PTC material, electric resistance increases to infinity, allowing immediate cessation of charging and discharging current when the temperature of the battery is higher than the threshold temperature. In general, the PTC material threshold temperature is set at about 100° C. (the temperature is also referred to as a “trip temperature”). The trip temperature is lower than the shut down temperature of the separator interposed between the positive electrode and the negative electrode. Therefore, when over-current occurs, the PTC device prevents the temperature from increasing. When it is not possible for the PTC device alone to prevent the temperature from increasing, the separator is shut down to prevent thermal runaway.
Additionally, a protective circuit module may be mounted in the secondary battery to prevent overcharge and over-discharge. The protective circuit module commonly includes a circuit board, a plurality of electronic elements mounted on the circuit board, a charging switch, and a discharging switch. Furthermore, the protective circuit module is commonly mounted on an outer surface of the secondary battery and molded by a resin.
In a conventional secondary battery, because the PTC device and protective circuit module are mounted in the secondary battery during the pack assembly process, the mountability and configurability of the PTC device and protective circuit module deteriorate. For example, the PTC device is connected to electrode tabs protruding from the secondary battery and to the protective circuit module using a conductive lead, resulting in the electrode tabs and conductive leads being folded multiple times to minimize their volume. As a result, the PTC device is not attached adjacent to the protective circuit module or the secondary battery. Therefore, when the temperature of the secondary battery increases, a delay may occur before the PTC material is activated.
In a conventional secondary battery, the PTC device and the protective circuit module are molded by a resin so as to be integrated with the secondary battery. The protective circuit module is designed to not protrude from the resin molding. Therefore, it is difficult to accurately position electrode terminals in the protective circuit module, resulting in the resin being formed in undesired positions with respect to the electrode terminals. When regions of the electrode terminals are covered with resin, the electrode terminals may not electrically connect to an external charger or an external system.